The goal of the proposed research is to study the regulation of expression of a eucaryotic genetic locus that plays a central role in the development of a tissue. We propose to study the regulation of the expression of the zein gene locus during endosperm development in Zea mays. The developing endosperm tissue of maize offers a favorable system since the synthesis of its storage proteins represents the one time expression of only a few genes in which massive amounts of protein are synthesized in a short period of time. The objectives of the proposed research are to: 1. prepare, characterize, and clone a cDNA copy of the zein mRNA; 2. determine the number of copies of the zein gene per genome in various tissues of the maize plant. In particular, to determine the number per genome in endosperm tissue during the course of its development; 3. measure the level of zein mRNA transcripts in various tissues of the maize plant and at various stages of endosperm development; determine the effect, if any, of endosperm mutants on zein mRNA transcription levels; 4. isolate chromatin from various tissues of the maize plant and at various stages of endosperm development. Determine by in vitro transcription the availability of the zein locus for transcription of zein mRNA; and 5. determine, by in vitro chromatin reconstitution what component(s) of chromatin control(s) the availability of the zein locus for transcription of zein mRNA sequences.